The prior art of lifting raw deepsea mineral resources mined at the deepsea floor from the sea floor to the sea surface involves two basic methods: Continuous Line Bucket (CLB) and hydraulic lifts.
CLB is a method of mining and lifting raw cobalt-rich crusts distributed on the sea floor at a water depth of 800.about.2,400 m with many buckets which are attached to a long loop of rope in regular intervals. If the water depth is deeper than 2,400 m, this method will be difficult, and besides it has disadvantages such as small lifting capacity.
Hydraulic lifts are methods of lifting raw manganese nodules concentrated widely in the Clarion-Clipperton zone of the northeastern Pacific Ocean at a water depth of 4,000.about.6,000 m using hydraulic power through lifting pipes to the sea surface. These are still classified into three methods as follows.
The first is an air-lift method of lifting raw manganese nodules to the sea surface by flowing high compressed air in the lifting pipe through air-lift jet units situated at a water depth about 2,000 m from air compressors on a marine ship. This method has the advantage of easy maintenance of air compressors situated on the marine ship, but on the other hand it has the disadvantage of large power consumption by them.
The second method is a centrifugal pump lifting method of lifting raw manganese nodules to the sea surface by operating high head/multiple-stage/centrifugal submersible pumps situated in the lifting pipe. This method makes it difficult to maintain centrifugal pumps which are situated at a water depth of at least 1,000 m, and has the advantage of smaller power consumption than the above air-lift method, but it also has the disadvantage of large power consumption.
The third method is a high density slurry pumping and lifting method of lifting a highly dense slurry mixed with sea water through the lifting pipe to the sea surface, the slurry being produced from raw manganese nodules ground by a crusher situated on the deepsea floor and fed into a piston pump also situated there. The advantage of this method is that the lifting pipe diameter can be smaller than those of the above air-lift and centrifugal pump lifting methods when lifting volumes are the same, but this method will require new development of reliable sea floor units (crusher, piston pump) and has the disadvantage of large power consumption.